如何防止构造一个类的对象？

class MyClass {
private:
    MyClass() {}
};

class MyClass {
public:
    MyClass() = delete;
};

class MyClass {
public:
    static MyClass* createInstance() {
        return new MyClass();
    }
private:
    MyClass() {}
};

class MyClass {
public:
    static MyClass& getInstance() {
        static MyClass instance;
        return instance;
    }
private:
    MyClass() {}
    MyClass(const MyClass&) = delete;
    MyClass& operator=(const MyClass&) = delete;
};

class MyClass {
private:
    MyClass() {}
    friend class FriendClass;
};

class FriendClass {
public:
    MyClass createMyClass() {
        return MyClass();
    }
};